Sfumato is a painting technique for softening the transition between colors so that there are no harsh lines. Subtle layers of paint are used to create a blurry, cloudy quality that gradually fuses one color into another. This technique was famously used by Leonardo da Vinci.
The key to Sfumato is to use very thin layers of paint, applied slowly and with great precision. The artist must have a light touch and be patient in order to create the desired effect. This technique can be used for both oils and watercolors, but it is most commonly associated with oil painting.